Multi-function products with light weights, slim shapes and small sizes have become the mainstream in the market as the technology is developed. Accordingly, the operation voltage of the internal circuit of a single technology product is reduced, and the number and types of circuits or integrated circuit chips are required more.
Generally, the voltage level shift among integrated circuits with different voltage levels is performed through a voltage level shift circuit. A typical voltage level shift circuit usually receives the signal of an IC internal device from a low voltage device, passes the signal through a medium voltage device and then a high voltage device, and outputs the signal from the high voltage device.
The medium voltage device of a known voltage level shift circuit has the same size, structure and components as the high voltage device of the same, and the gate dielectric layer of the medium voltage device is as thick as that of the high voltage device. However, during the operation, the saturated current of the medium voltage device is small and the performance of the same is bad. Further, the occupied chip area becomes greater due to the larger size of the high voltage device and the medium voltage device, so that the chip reduction becomes difficult and a higher chip cost is caused.